1. Field of the Invention
The present invention relates to a spectrally sensitized silver halide photographic emulsion and, more particularly, it relates to a silver halide photographic emulsion spectrally sensitized by using a combination of at least two or more sensitizing dyes.
2. Description of the Prior Art
In spectrally sensitizing silver halide emulsions, it is known that the combination of a certain sensitizing dye and another sensitizing dye or a compound other than a sensitizing dye markedly increases the efficiency of spectral sensitization to provide high sensitivity. This effect is called supersensitization. Various combinations of sensitizing dyes have been suggested for the purpose of supersenitization. However, it is also known that, with respect to a combination of two or more sensitizing dyes providing supersensitization, the dyes are so selective together that it is extremely difficult to predict that a supersensitizing action will be obtained from the chemical structure of the sensitizing dyes.
On the other hand, supersensitization using a combination of two or more sensitizing dyes often causes a reduction in spectral sensitivity in a specific spectrally sensitized wavelength region, an increase in fog, a deterioration of stability with time such as a reduction in sensitivity or increase in fog during or after production of the light-sensitive materials, a deterioration of latent image stability between photographic exposure and development, and like defects. Achieving supersensitization using a combination of sensitizing dyes which does not cause these detrimental actions has been an important subject in the field of producing light-sensitive materials.